Transmission for a vehicle

Abstract

A transmission for a vehicle comprises a mechanical stepped gearbox (6) in front of which a hydraulic torque converter (5) is arranged. The torque converter (5) comprises a turbine wheel (19) which is connected to a turbine shaft (21). An input shaft (25) of the gearbox (6) is connected in a drive power-transmitting manner to the turbine shaft (21). In addition, a brake (34) is connected to the turbine shaft (21) or the input shaft (25), in which respect, on starting-up, the input shaft (25) can be stopped in order to permit engagement of a starting gear without the need to produce drive power interruption by means of a conventional clutch. The brake (34) is also used when changing-up for synchronization of the gearbox (6) together with an electrical control unit (32) for engine regulation. This allows the gear-changing in a mechanical, unsynchronized stepped gearbox to be carried out in a simple manner.

We claim: 
     
       1. A transmission for a vehicle, said transmission comprising: a stepped gear box having an input shaft and an output shaft and a plurality of shiftable gear wheels coupled therebetween;   a hydrodynamic torque converter having an input for receiving driving power from a power source and an output shaft, said output shaft of said torque converter being coupled in a drive power transmitting relationship to said input shaft of said stepped gear box;   said torque converted including a turbine wheel which is connected in a drive power transmitting relationship to said output shaft of said torque converter via a free wheel;   a brake connected to at least one of said output shaft of said torque converter and said input shaft of said stepped gear box; and   an electrical control unit for controlling both gear shifting operations of said stepped gear box and the operation of said brake, said electrical control unit causing said brake to stop the rotation of said stepped gear box input shaft when a gear change operation is to take place in said stepped gear box.   
     
     
       2. A transmission according to claim 1, wherein said stepped gear box includes a plurality of pairs of gear wheels, said gear wheels being disposed respectively on a main shaft and at least one side shaft, said gear wheels having a plurality of different gear ratios, said pairs of gear wheels being selectively engaged by means of dimensionally fixed clutch members. 
     
     
       3. A transmission according to claim 2, wherein said electrical control unit controls said gear changing operations of said stepped gear box by causing said fixed clutch members to selectively engage respective pairs of said gear wheels. 
     
     
       4. A transmission according to claim 1, wherein said brake includes electrohydraulic servo members whose operation are controlled by said electrical control unit. 
     
     
       5. A transmission according to claim 4, wherein said electrical control unit causes said brake to stop the rotation of said stepped gear box input shaft before said electrical control unit shifts said gear box from a neutral position to a starting gear position. 
     
     
       6. A transmission according to claim 4, wherein said electrical control unit controls said electrohydraulic servo members of said brake, said brake is activated first by taking up mechanical play in the brake without applying braking power to said at least one of said output shaft of said torque converter and said input shaft of said stepped gear box and then by subsequently applying braking power to said at least one of said output shaft of said torque converter and said input shaft of said stepped gear box. 
     
     
       7. A transmission according to claim 1, further comprising a planetary gear having an input coupled to said power source and a pair of outputs, one of said outputs being coupled to said input of said hydrodynamic torque converter, the other of said outputs being coupled to said input shaft of said stepped gear box, said planetary gear dividing the drive torque applied to its input into a first part which is transmitted hydraulically via said torque converter to said input shaft of said stepped gear box and a second part which is transmitted mechanically to said input shaft of said stepped gear box. 
     
     
       8. A transmission according to claim 7, wherein said planetary gear comprises: a planetary wheel connected to said input of said planetary gear;   a sun wheel connected in a drive power transmitting relationship to said input of said hydraulic torque converter;   a ring wheel mechanically connected in a drive power transmitting relationship to said stepped gear box input shaft whereby said planetary gear transmits power to said stepped gear box in two parts, one of said parts being transmitted hydraulically to said stepped gear box via said torque converter, the other of said parts being transmitted to said stepped gear box input shaft through direct mechanical connection.   
     
     
       9. A transmission according to claim 8, wherein said sun wheel is connected to a second brake, said second brake being selectively controlled by said electronic control unit to selectively prevent rotation of said sun wheel at which time all of torque from said planetary gear input shaft is transmitted mechanically to said stepped gear box input shaft and said planetary gear acts as an overdrive gear. 
     
     
       10. A transmission according to claim 1, wherein said transmission does not include any mechanical plate clutch for interrupting the application of the drive power from said power source to said stepped gear box during said gear changing operations. 
     
     
       11. A transmission according to claim 1, wherein said electrical control unit includes means for detecting that a drive mode selector has been placed in a drive mode, and said electrical control unit controls: means for preventing rotation of said input shaft of said stepped gear box;   means for engaging a starting gear in said stepped gear box; and   means for releasing said input shaft of said stepped gear box so as to permit said input shaft to rotate.   
     
     
       12. A transmission according to claim 11, wherein said electrical control unit includes means for activating said brake in order to prevent the rotation of said input shaft of said stepped gear box comprising: means for causing said brake to take up mechanical slack without actually preventing rotation of said input shaft of said stepped gear box after said electrical control unit has detected that a drive mode selector has been placed in a drive mode; and   means for causing said brake to actually prevent rotation of said input shaft of said stepped gear box only after said electrical control unit has determined that either no gear is engaged in the stepped gear box, or that the gear box is in a neutral position.   
     
     
       13. A transmission for a vehicle, said transmission comprising: a stepped gear box having an input shaft and an output shaft and a plurality of shiftable gear wheels coupled therebetween;   a hydrodynamic torque converter having an input shaft for receiving driving power from a power source and an output shaft, said output shaft of said torque converter being coupled in a drive power transmitting relationship to said input shaft of said stepped gear box;   an electrical control unit for controlling both gear shifting operations of said stepped gear box and the operation of a hydraulic disc brake, said electrical control unit causing said brake to stop the rotation of said stepped gear box input shaft when a gear change operation is to take place in said stepped gear box;   said brake being connected for braking at least one of said output shaft of said torque converter and said input shaft of said stepped gear box, and said brake being supplied with a hydraulic fluid upon activation and having electrohydraulic servo members, each comprising two solenoid valves connected to and operated by said electrical control unit, one of said solenoid valves determining whether or not said hydraulic fluid is applied to said disc brake, the other of said solenoid valves controlling the pressure at which said hydraulic fluid is applied to said hydraulic disc brake.   
     
     
       14. A transmission according to claim 13, wherein said brake is activated first by applying a low pressure taking up mechanical play in the brake without applying braking power, and then by subsequently applying a high pressure, thereby causing said brake to apply braking power. 
     
     
       15. A transmission according to claim 14, wherein said low pressure is less than one bar and said high pressure is at least five bars. 
     
     
       16. A transmission according to claim 13, wherein said brake includes a disc firmly connected to at least one of said output shaft of said torque converter and said input shaft of said stepped gear box, and two opposing calipers, and when said electrical control unit controls said solenoid valves, said hydraulic fluid is first applied to said brake at a relatively low pressure to take up slack between said two calipers and said disc, and is then applied to said brake at a relatively high pressure to force said two calipers into braking contact with said disc. 
     
     
       17. A transmission for a vehicle, said transmission comprising: a stepped gear box having an input shaft and an output shaft and a plurality of shiftable gear wheels coupled therebetween;   a hydrodynamic torque converter having an input shaft for receiving driving power from a power source and an output shaft, said output shaft of said torque converter being coupled in a drive power transmitting relationship to said input shaft of said stepped gear box;   a brake connected to at least one of said output shaft of said torque converter and said input shaft of said stepped gear box;   an electrical control unit for controlling both gear shifting operations of said stepped gear box and the operation of said brake, said electrical control unit causing said brake to stop the rotation of said stepped gear box input shaft when a gear change operation is to take place in said stepped gear box; and   a planetary gear having an input coupled to said power source and a pair of outputs, one of said outputs being coupled to said input of said hydrodynamic torque converter, the other of said outputs being coupled to said input shaft of said stepped gear box, said planetary gear dividing the drive torque applied to its input into a first part which is transmitted hydraulically via said torque converter to said input shaft of said stepped gear box and a second part which is transmitted mechanically to said input shaft of said stepped gear box.   
     
     
       18. A transmission according to claim 17, wherein said planetary gear comprises: a planetary wheel connected to said input of said planetary gear;   a sun wheel connected in a drive power transmitting relationship to said input of said hydraulic torque converter;   a ring wheel mechanically connected in a drive power transmitting relationship to said stepped gear box input shaft whereby said planetary gear transmits power to said stepped gear box in two parts, one of said parts being transmitted hydraulically to said stepped gear box via said torque converter, the other of said parts being transmitted to said stepped gear box input shaft through direct mechanical connection   
     
     
       19. A transmission according to claim 18, wherein said sun wheel is connected to a second brake, said second brake being selectively controlled by said electronic control unit to selectively prevent rotation of said sun wheel, at which time all of the torque from said planetary gear input shaft is transmitted mechanically to said stepped gear box input shaft, and said planetary gear acts as an overdrive gear. 
     
     
       20. A method for operating the transmission of a vehicle of the type which includes a stepped gear box having an input shaft and an output shaft and a plurality of shiftable gear wheels coupled therebetween; a hydrodynamic torque converter having an input for receiving driving power from a power source and an output shaft, said output shaft of said torque converter being coupled in a drive power transmitting relationship to said input shaft of said stepped gear box; said torque converter includes a turbine wheel which is connected in a drive power transmitting relationship to said output shaft of said torque converter via a free wheel; and   a brake connected to at least one of said output shaft of said torque converter and said input shaft of said stepped gear box, said method comprising the steps of:   determining when a gear changing operation is to take place in said stepped gear box; and   causing said brake to stop said stepped gear box input shaft when a gear changing operation is to take place in said stepped gear box.   
     
     
       21. The method of claim 20, wherein said stepped gear box includes a plurality of pairs of gear wheels, said gear wheels being disposed respectively on a main shaft and at least one side shaft, said pairs of gear wheels being selectively engaged by means of dimensionally fixed clutch members, and wherein said method further comprises the step of causing a gear changing operation to take place in said stepped gear box by causing said fixed clutch members to selectively engage respective pairs of said gear wheels. 
     
     
       22. A method according to claim 20, wherein said brake includes electrohydraulic servo member, and wherein said step of causing said brake to stop the rotation of said stepped gear box input shaft comprises the steps of: taking up mechanical play in the brake without applying braking power to said at least one of said output shaft of said torque converter and said input shaft of said stepped gear box; and thereafter   applying braking power to said at least one of said output shaft of said torque converter and said input shaft of said stepped gear box.   
     
     
       23. A method according to claim 22, wherein said brake is a hydraulic disc brake including first and second opposing calipers, and a disc firmly connected to at least one of said output of said torque converter and said input shaft of said stepped gear box, and wherein said step of causing said brake to stop the rotation of said stepped gear box input shaft comprises the steps of: applying hydraulic fluid to said disc brake at a relatively low pressure so as to take up slack between said two calipers; and thereafter   applying hydraulic fluid to said disc brake at a relatively high pressure so as to force said two calipers into braking contact with said disc.   
     
     
       24. A method according to claim 23, wherein said low pressure is less than one bar and said high pressure is at least five bars. 
     
     
       25. A method according to claim 23, wherein said gear shifting apparatus operations of said stepped gear box are carried out by: detecting that a drive mode selector has been placed in a drive mode;   activating said brake in order to prevent rotation of said input shaft of said stepped gear box;   engaging a starting gear in said stepped gear box; and   causing said brake to release said input shaft of said stepped gear box so as to permit said input shaft to rotate.   
     
     
       26. A method according to claim 25, wherein said electrical control unit activates said brake in order to prevent the rotation of said input shaft of said stepped gear box by; first causing said brake to take up mechanical slack without actually prevent rotation of said input shaft of said stepped gear box after said electrical control unit has detected that a drive mode selector has been placed in a drive mode; and thereafter   causing said brake to actually prevent rotation of said input shaft of said stepped gear box only after said electrical control unit has determined that either no gear is engaged in the stepped gear box, or that the gear box is in a neutral position.